A scintillator is a special material that exhibits scintillation—the property of luminescence when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate, in other words they reemit the absorbed energy in the form of light.
A scintillation detector or scintillation counter is obtained when a scintillator is coupled to a light sensor such as a photomultiplier tube (PMT), charge-coupled devices (CCD), PIN photodiodes, and the like. The light sensor will absorb the light emitted by the scintillator and reemit it in the form of electrons via the photoelectric effect. The subsequent multiplication of those electrons (sometimes called photo-electrons) results in an electrical pulse that can be analyzed and provides meaningful information about the particle that originally struck the scintillator. In this way, the original amount of absorbed energy can be detected or counted.
The term “plastic scintillator” typically refers to a scintillating material where the primary fluorescent emitter, called a fluor, is suspended in a solid polymer matrix. While this combination is typically accomplished through the dissolution of the fluor prior to bulk polymerization, the fluor is sometimes associated with the polymer directly, either covalently or through coordination, as is the case with many Li6 plastic scintillators. Polyethylene naphthalate has been found to scintillate without any additives and is expected to replace existing plastic scintillators due to its higher performance and lower price.
The advantages of plastic scintillators include fairly high light output and a relatively quick signal, with a decay time between 2-4 nanoseconds. The biggest advantage of plastic scintillators, though, is their ability to be shaped, through the use of molds or other means, into almost any desired form with a high degree of durability.
In the field of medical radiation therapy, plastic scintillation detectors or “PSDs” are used to convert radiation energy into light energy, and the light photons are counted to accurately determine the radiation dose. The scintillating plastic must transfer its photons to a device that can read them, which is commonly done by coupling one or more scintillating fibers to one or more plastic optical fibers (POF). The POF is then connected to a device that can read and analyze the optical output.
A PSD sensor or dosimeter is made of three major building blocks: the scintillating probe, a light guide and a photodetector—together called the “optical chain.” The linearity between the dose and light output depends on each component in the optical chain, each stage added in the path of the optical photons leading to a decrease in efficiency. First, the visible light produced in the scintillator must travel (through internal reflection) toward the exit face of the scintillator and into the light guide (e.g. an optical fiber) (collection efficiency of about 5%). The interface between various components, e.g. scintillator to optical guide, is also a source a loss and the coupling efficiency is generally around 75-85%. Optical fibers, in particular the water-equivalent and flexible plastic types, are often used because of their enhanced light transport properties. Light attenuation in an optical fiber guide is generally less than 20% over a few meters. The output of a light guide must then be captured by a photodetector. Depending on whether the coupling to the photodetector is direct or not, passing through filters or a lens (or a combination thereof), the coupling efficiency can be as low as 5% and as high as 90%. Finally, the photodetector itself possesses an intrinsic efficiency (quantum efficiency), which can vary from 20% to 90%. The overall efficiency over the complete optical chain is thus only of a few percent and optimization of each component is important.
Manufacturing a high volume of such PSD sensor cables is difficult because an accurate and repeatable connection of the plastic scintillator fiber to the plastic optical fiber is required. The problem arises from working with small diameter optical fibers that must be constructed accurately, yet at a low cost. Thus, what are needed in the art are netters methods if making PSD sensors, better PSD sensors, and improved treatment methodologies that are provided by improved PSD sensor.